1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a structure which dissipates heat from one side.
2. Description of the Background Art
In recent times, a power electronics for the purpose of saving energy is expected to develop greatly. A power module serving as a semiconductor device packaging a power semiconductor element is adopted as the central part of a power electronics device to greatly contribute to the development.
A power module, which is basically formed of an insulated gate bipolar transistor (IGBT) including a silicon for a base material and a diode, is mainly used in recent days. A power semiconductor element is improved with the times. However, for further development of a power electronics, it is required to be able to control a larger amount of current with reliability. The best method to satisfy the requirement is to change the base material of a power semiconductor element from silicon to silicon carbide (SiC). SiC is desired to be applied to a power module because the material itself has a high insulation breakdown voltage, SiC is able to operate in a high temperature of 300° C. without a thermal runaway, and SiC has approximately one-tenth power loss of silicon during operation comparing in the same current density.
A general power module on a back side exposes a base plate formed of a highly heat conductive material such as copper. The base plate is mechanically joined to a heat dissipation fin by a fastening member such as a screw. The heat dissipation fin is made of aluminum, copper, and the like. In addition, a heat dissipation grease is applied between the base plate and the heat dissipation fin to decrease thermal contact resistance.
When the power module is operated, heat is generated as a loss (product of current and voltage) of the power semiconductor element. This heat is dissipated to the outside by the heat dissipation fin through the base plate. In this manner, in the structure which dissipates heat from the back side of the power module, it is important to efficiently conduct the heat generated in the power semiconductor element to the base plate.
The power module basically has an insulating structure, thereby usually having an insulating layer (insulating substrate and insulating sheet) on an upper part of the base plate. In general, an insulating layer has a great thermal resistance, thereby deteriorating heat dissipation in this portion. To solve this problem, heat conductivity of the insulating layer itself has been increased, the thickness thereof has been reduced, and the like.
For example, in Japanese Patent Application Laid-Open No. 2000-174180, a heat dissipation plate is provided on both of the lower side and the upper side of the semiconductor element to efficiently dissipate heat.
However, increasing heat conductivity of an insulating substrate itself makes the material itself quite expensive, resulting in a cost increase. Moreover, reducing the thickness of the insulating substrate decreases an allowable strength of the insulating substrate, resulting in a fracture in the insulating substrate and a shortage of the insulation breakdown voltage.